Method of shipping frozen food



United States Patent 3,225,553 METHOD OF SHEPPING FROZEN FOOD Willard L.Morrison, Lake Forest, Ill., assignor to The Union Stock Yard andTransit Company of Chicago, Chicago, Ill., a corporation of Illinois NoDrawing. Filed Jan. 21, 1963, Ser. No. 252,594 5 Claims. (Ci. 2-'76)This is a continuation-impart of my cop-ending application Serial No.659,473, filed May 16, 1957, and entitled Method of Shipping FrozenFood, now abandoned.

My invention relates to improvements in method of shipping frozenfoodstuffs and has for one object to provide a method for :greatlyincreasing the effectiveness of presently used means for shipping frozenfoodstuffs in transit.

Another object of my invention is to greatly increase the effectivenessof the shipment of foodstuffs in refrigerator cars by rail and the like.

It is customary in connection with the shipment of frozen foods, forexample, from California to the east coast, to charge the ice bunkers ofrefrigerator cars at a central point with ice and salt. The empty car isthen discharged from the assembly point to the loading dock of thefrozen food manufacturer. By the time the car reaches the dock, it hasbeen to some extent precooled by cold air circulating in the car fromthe salt and ice bunker. Such circulation may be by gravity or by axledriven fan.

The solid ice in the bunker melts at substantially zero degrees F. andthe temperature of the ice approaches that low point and so air currentssomewhat above zero circulate through the car to cool the interiorthereof. The temperature, of course, is never as low as zero. First,because the ice and salt mixture can only be at zero and second, becausethere is substantial heat infiltration through the insulation of the carand through air leakage because the car can never be gastight.

As a result, the frozen food at temperatures perhaps zero degrees F.,perhaps above or perhaps below that point, is loaded into a car, thetemperature of which even though it has been chilled is usually abovethe temperature of the foodstuff but, of course, far below ambienttemperature. The loaded car is then returned to the assembly point.There because during its trip to the load ing dock and return, much ofthe salt and ice is melted away, the car is recharged with ice and saltand started on its way to the east. As the car travels and as the iceand salt melts, the amount of salted ice available as a coolantgradually decreases and so the effectiveness of the cooling in the cargradually decreases and the temperature of the contents gradually riseabove zero. This is disadvantageous because it is a well known fact thatthe foodstuffs ought to be kept at zero or below. That is impossiblebecause the ice and salt cannot provide a temperature below zero but canonly provide a temperature substantially above it.

I propose, without any change in the equipment heretofore used, to firstcharge the bunker with the usual amount of ice and salt and immediatelythereafter to discharge onto the bunker ice, liquid nitrogen atatmospheric pressure and so at substantially -320 F. The ice and salt atzero degrees F. will furnish the latent heat to vaporize this liquidnitrogen as the temperature of the ice drops to a point, depending uponthe volume of liquid nitrogen discharged into the bunker.

As this liquid nitrogen evaporates, it will be immediately withdrawnfrom the car at a temperature little if any below the boiling point ofliquid nitrogen at atmospheric pressure, namely '320 F. and thereliquefied nitrogen can again be used as a refrigerant.

Patented Dec. 28, 1965 There may be some rise in temperature of thegaseous nitrogen by heat exchange with the interior of the car and thiswill tend to assist the ice in the cooling function.

The car will then be forwarded with this superchilled salt and ice tothe loading dock. The same air currents cooled by the ice will cool theinterior of the car but under ordinary circumstances, the ice will nothave time to rise in temperature to zero degrees, the melting point, sothere will be no loss of salt and ice on the way to the loading dock butthe car being chilled by a source of cold far below zero will be at atemperature also below zero.

When the car is then charged with frozen food at approximately zero, thefood will be exposed to an atmosphere colder than itself and will eithernot rise in temperature and may usually fall somewhat in temperature onits way back to the distribution point.

If the amount of ice and the temperature to which it is reduced areproperly selected, the ice will still be below zero when it gets backto. the central distribution point but will be at a temperature higherthan the starting temperature.

At that point, since the destination of the car will then be known andsince the approximate time of travel will then be known, all that isnecessary is to add more liquid nitrogen to lower the bunker icetemperature down to the point at which it will reach destination eitherbefore the ice had melted or if longer time is required before the icebunker can again be recharged.

The temperature of the foodstuffs will thus remain at zero or below forthe major part of the trip and only toward the end of the trip when theice has finally reached, if it does reach it, a temperature of zerodegrees F. is the foodstuff exposed to a temperature above zero.

The specific heat of ice is in the order of .5. The specific heat of thefoodstuffs is in the order of .383. Thus the ice furnishes a much moreeffective source of cold than does the foodstuffs itself and since thebunker area or bunker volume is only a small part of the car, it is easyto discharge the liquid nitrogen into the bunker and withdraw it beforeit has gained too much temperature above -320 P. so that thereliquefaction of the nitrogen after it has done its work is apracticable operation.

Under these circumstances, it might be suflicient merely to charge thebunker with salt and ice at the central point, then to ship it to theloading dock, fill it in the usual way and return it to the distributionpoint to start it on its way to destination. Under these circumstances,the ice bunker would be charged to replace that which was lost intransit to and from the loading dock and would then superchill the icewith liquid nitrogen but this would require two icings at thedistribution point whereas in the first instance, the ice is chilled tothe point where it will not melt before it returns to the distributionpoint, only one icing but two superchillings will be required. Which ofthe two alternatives is most economical would, of course, depend uponthe circumstances of use, distances, time, etc.

When the car has reached its destination and has been unloaded, havinghad the benefit of the superchill effect during its travel with frozengoods, even though there is no nitrogen reliquefaction or liquidnitrogen supply at destination, the use of the nitrogen to superchillthe ice has not in any way interfered with the normal usefulness of therefrigerator car under usual salt and ice conditions so my method caneasily be superposed on the usual ice cooled refrigerator car withoutany change whatever in that car, with the mere addition of a source ofliquid nitrogen, preferably accompanied by the reliquefaction of thegaseficd nitrogen.

When the cold dry icebecause when below zero it does not melt and so isdryhas finally risen to zero degrees F., then and then only does thechemical salt ice action come into play and one thing that thesuperchilling effect of the liquid nitrogen accomplishes is a delay ofthe start of the chemical reaction of salt and ice. So I propose to usethe salt and ice first as a storage for cold without any chemicalreaction or any change of the material except a rise in temperature andlater as a supply of cold resulting from the melting of the ice andsalt.

When the ice in the bunker has been cooled below the melting point zerodegrees F. and is dry because it is not melting, it will, of course,pick up somevmoisture from the ambient air or from the air in the carbecause vapor migration moves toward the cold spot. This may result insome slight expansion in weight and volume of the ice but as the icetemperature rises and as long as the ice temperature is below that ofthe air surrounding it this sitnation will prevail but as soon as theice reaches zero and begins to melt, water runs off the ice and thevolume or weight of the ice will then commence to decrease.

In my invention under ordinary circumstances, I will not rely on thecooling elfect of the ice and salt, as above zero degrees F. My solutionof the problem will be entirely effective provided the car reachesdestination with the food and the ice at the same temperature in theorder of zero degrees The presence of the salt and the ice serves as asafety device if the trip takes too long or the temperature to which thecar is exposed is inordinately high and if the temperature of the icerises to and above zero, then I still will have the additionalprotection available until the ice is all melted but this protection isa protection which still involves an undesirable though perhaps notfatal rise in the temperature of the contents of the car.

Instead of liquid nitrogen I may use other inert liquefied .gases havingan extremely low boiling point temperature at atmospheric pressure, suchas liquefied air.

I claim:

1. In the method of shipping perishable products in a transport having astorage space of large capacity for housing the perishable products andice bunkers alongside said storage space but separate and aparttherefrom for refrigeration of air circulated through the storage space,the steps of filling said ice bunkers with ice, and contactingsaid icewith a liquefied gas selected from the group consisting of air andnitrogen having a boiling point at atmospheric pressure of less than 300F. to superfreeze the ice to temperatures below freezing.

2. In the method of shipping perishable products in a transport having astorage space of large capacity for housing the perishable product-s andice bunkers alongside said storage space for refrigeration of aircirculated through the said storage space, the steps of filling the icebunkers with ice and salt, and applying a liquefied gas selected fromthe group consisting of liquefied air and liquefied nitrogen to the icein the ice bunkers to superfreeze the ice to temperatures substantiallybelow freezing.

=3. The method of shipping perishable products in a transport having astorage space of large capacity for housing the perishable products andice bunkers alongside said storage space for refrigeration of aircirculated through the said storage space, the steps of filling the icebunkers with ice, treating the ice in the ice bunkers with liquidnitrogen until the temperature of the ice has been reduced to far belowfreezing.

4. The method as claimed in claim 3, in which the ice in the ice bunkersis treated with the liquefied nitrogen before the storage space isfilled with the perishable product.

5. The method as claimed in claim 3, in which the ice in the ice bunkersis treated with liquefied nitrogen after the storage space has beenfilled with the perishable product.

References Cited by the Examiner UNITED STATES PATENTS 2,337,600 12/1943Harris 6276 2,353,909 7/1944 Lager 6262 2,479,821 8/ 1949 Deutsch 62--622,479,840 8/ 1949 Johnson 6262 2,501,141 3/1950 Plummer 6262 2,5 02,5274/ 1950 McFarlan 62-67 2,516,166 7/1950 Wiczer 62l 2,784,567 3/1957Reynolds 6263 EDWARD J. MICHAEL, Primary Examiner.

1. IN THE METHOD OF SHIPPING PERISHABLE PRODUCTS IN A TRANSPORT HAVING ASTORAGE SPACE OF LARGE CAPACITY FOR HOUSING THE PERISHABLE PRODUCTS ANDICE BUNKERS ALONGSIDE SAID STORAGE SPACE BUT SEPARATE AND APARTTHEREFROM FOR REFRIGERATION OF AIR CIRCULATED THROUGH THE STORAGE SPACE,THE STEPS OF FILLING SAID ICE BUNKERS WITH ICE, AND CONTACTING SAID ICEWITH A LIQUEFIED GAS SELECTED FROM THE GROUP CONSISTING OF AIR ANDNITROGEN HAVING A BOILING POINT AT ATMOSPHERIC PRESSURE OF LESS THAN-300*F. TO SUPERFREEZE THE ICE TO TEMPRATURES BELOW FREEZING.